Working fluids, such as lubricating oils and hydraulic fluids, are important components of a wide variety of mechanical systems in which they provide one or more functions such as lubricating moving parts, transferring force or energy on the mechanical system, protecting parts against wear or even a combination of these.
These fluids typically consist of a hydrocarbon, base oil formulated with numerous additives selected to enhance one or more performance characteristics of the fluid.
With use over time these fluids may become contaminated with substances with which they come into contact, by the ingress of foreign substances in the mechanical system, by oxidation of the base oil and chemical decomposition of the additives used in the formulated fluids. The net result is a decrease in the performance characteristics of the fluid with the concomitant negative impact on the mechanical system using the fluid.
Therefore, in many industrial environments regular fluid analysis by common laboratory methods is a standard modus operandi. This necessitates running a sample of the fluid and transporting it, typically off-site, for analysis. This procedure normally takes at least three full days before the requisite analysis is completed and a report can be obtained. Such a time lag is highly undesirable.
The art is replete with proposed methods for the on-line evaluation of the quality of lubricants, many of which are based on electrical measurements, such as the dielectric constant or impedance of the fluid, with the measurements being taken most often at one, and sometimes two, discrete and fixed frequencies. Experience has shown, however, that these methods are not entirely satisfactory. For example, at some frequencies and at low temperatures the electrical property of the fluid being measured is insufficiently sensitive to give a reliable indication of the condition of the fluid and even if sufficiently sensitive, the frequency chosen may not necessarily provide an accurate indication of the condition of the lubricant. Also, the wires and other components used for making electrical measurements can produce spurious effects that obscure or distort the electrical properties of the fluid. Moreover, the best frequency for optimum sensitivity is highly dependent on the properties of the working fluid and measurements typically taken at discrete and fixed frequencies are not optimized for a specific working fluid.
Additionally, many working fluids have extremely low conductivities. For example, industrial oils typically have significantly lower conductivities than internal combustion engine lubricants undoubtedly due to the higher viscosity and lower additive concentrations of the industrial lubricants. Consequently the ability to employ electrical measurements based on fixed frequency measurements developed for engine lubricants to determine the quality or condition of that have relatively low conductivities such as industrial oils is quite problematic.
Thus there remains a need for improvements in determining the condition of a working fluid such as a lubricant.
An object, therefore, of the present invention is to provide a method for detecting the depletion of performance additives in a lubricant.
Another object is to provide an electrical measurement method for determining the condition of low conductivity industrial oil.
Still another object is to provide for improving the sensitivity in the electrical measurement for determining the condition of working fluids.
These and other objects will become apparent from the description which follows.